Tap here to read more about Deck Spindle for Simplicity 3900 5901798 5901799 61″ 72″ / 84003242 5413009 3x. Premium Quality Replacement Part. 3900 (5900598) – Massey Ferguson 72″ Zero-Turn Mower, 36hp Briggs & Stratton 72″ Mower Deck – Housing. 5901798 – Simplicity Cobalt LE 61 Zero-Turn Mower, 37hp Briggs & Stratton. 5901799 – Simplicity Cobalt LE 72 Zero-Turn Mower, 37hp Briggs & Stratton. MANUFACTURED TO MEET OR EXCEED OEM PERFORMANCE.